Apple's iPod is partly to blame for the collapse of the music industry, according to a report Friday from researcher eMarketer.

The Mac maker helped set the tone for a "rat's nest of restrictions and incompatibilities" that have stalled the growth of digital music, according to Paul Verna, the author of the report.

Revenue in the music industry continues to decline in part because of consumer confusion, the report said.

A big part of the reason is music fans are asked to sort out the explosion of incompatible formats, players, restrictions, and retailers. That lack of simplicity  has slowed sales.

Apple has been a "double-edged sword" for the industry, the report said. Its closed system works well for iPod users, "but leaves many frustrated consumers outside of that system."

Digital rights management, or DRM, which restricts the number of places where consumers can copy their music, has also played a major role in hindering digital music sales, the report said.

In recent weeks the industry has moved to stop the bleeding caused by DRM by removing all DRM restrictions from a number of the major MP3 stores.

The music industry's long-term game plan was that digital downloads would gradually make up for falling CD sales. But it has not worked out that way. Digital downloads have not come anywhere near to making up for CD sales losses.

Numbers are not yet available for 2007, but the report expects the downward trend to continue through 2007 and perhaps through 2008.